Biomass, a renewable energy source, can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuels. Biofuels are derived from biomass and are intended to provide an alternative to petroleum fuels. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into thermal, chemical and biochemical methods.
Fossil fuels such as petroleum, natural gas and coal are typically formed through the processes of thermochemical conversion (TCC) from biomass buried beneath the ground.
TCC is a chemical reforming process of biomass in a heated and usually pressurized, oxygen deprived enclosure, where long-chain organic compounds break into short-chain hydrocarbons such as syngas or oil. TCC is a broad term that includes gasification, including the Fisher-Tropsch process, direct liquefaction, hydrothermal liquefaction and pyrolysis.
Pyrolysis is a heating process of dried biomass to directly produce syngas and/or oil. Both gasification and pyrolysis require dried biomass as feedstock and the processes occur in an environment higher than 600° C.
Hydrothermal liquefaction (HTL) is a technology for converting high-moisture waste biomass into energy dense “crude bio-oil” that can be used for direct combustion or refined for transportation grade fuels.
HTL, also called hydrous pyrolysis, is a process for the reduction of complex organic materials such as bio-waste or biomass into crude oil and other chemicals.
Hydrothermal Liquefaction (HTL) technique, which involves the application of heat and pressure on the biomass medium, has an advantage that the lipids and other organic components can be efficiently converted while the biomass is in wet condition. During HTL, high moisture biomass is subjected to elevated temperature (250-400° C.) and pressure (up to 225 bars) in order to break down and reform the chemical building blocks into crude bio oil. HTL of biomass gives only crude bio oil that needs to be further treated/refined to get finished crude oil products. The hydrothermal process breaks down bio macromolecules in the wet biomass and promotes heteroatom removal.
Some of the representative patent documents which suggest conversion of biomass to upgraded bio-oil via crude bio oil are discussed herein below.
US20120055077 suggests a method of producing an upgraded bio-oil from a wet biomass which involves heating the wet biomass at a first temperature (200 to 400° C.) and a first pressure (0.1 to 25 MPa) for a time period ranging from 10 to 200 minutes to form a crude bio-oil and heating the crude bio-oil and water at a second temperature and a second pressure for a time period of at least 30 minutes to form the upgraded bio-oil, wherein the second temperature is greater than the first temperature and is at least 300° C.
However, the process suggested in US20120055077 has the drawback that it requires stringent reaction conditions to be maintained throughout. As per the procedure suggested in US20120055077, the biomass is subjected to heat twice i.e. heating at a first temperature and at a first pressure followed by heating at a second temperature and at a second pressure. The first temperature and first pressure are below supercritical conditions of water; whereas the second temperature and second pressure are at or near supercritical conditions of water. In the first heating step, the reaction must be controlled in such a manner that at least a portion of the water present in the wet biomass remains in liquid phase throughout the step of heating to form the crude bio-oil. Further, in the second heating step, the crude bio oil is converted into upgraded bio-oil only in the presence of water; the crude bio-oil and water must be heated in such a manner that some water remains in the liquid phase or in a super-critical fluid phase throughout the step of heating to form the upgraded bio-oil. Still further, the catalysts employed in the process suggested by US 20120055077 are heterogeneous catalyst containing Pd/C, Pt/C, Ru/C, Ni/SiO2-Al2O3, sulfided CoMo/γ-Al2O3, zeolite, activated carbon, and combinations thereof.
Considering the complexity associated with the suggested process, there is a need for a simple, energy efficient, time saving and high yielding process for the conversion of biomass into crude bio oil and its up-gradation into bio-oil.